The US has the highest incarceration rate in the world. Each year in the US, jails incarcerate 12 million people, most of whom are either awaiting sentencing or serving out short sentences. Persons of color are incarcerated at disproportionately high rates, and as a class, incarcerated persons have worse health than other US residents. Jail inmates shoulder a heavy burden of mental health conditions (64%), chemical dependency (68%), infectious diseases (14%) and other chronic conditions (45%). Custody in jail can be a time of heightened physical and emotional stress, and indeed myocardial infarction and suicide are the two most frequent causes of death during incarceration. The heavy burden of health problems and large size of this population in combination with generally short incarcerations and limited healthcare resources present formidable challenges addressing jail inmates? healthcare needs. These challenges may be particularly difficult for southern jails, which are often small-sized and located in rural, resource-limited communities whose populations have relatively high rates of poverty and disability compared to other US regions. In recent years, deaths occurring during incarceration have created heightened attention regarding jail health services, and in 2011 there was a broad national survey of jail inmates? self-reported health conditions. However, the broad inmate survey did not reflect acute care needs and was susceptible to self-report bias, while reported deaths are rare events that provide only limited insight into inmates? health and healthcare. Because of a variety of barriers, few studies have examined the delivery of healthcare for jail inmates. Robust indicators of inmates? immediate healthcare needs?and the extent to which their needs exceed jail healthcare resources?could be used to target interventions to improve jail healthcare and reduce costs. A novel and potentially powerful indicator signaling that inmates? healthcare needs exceed jail healthcare resources is the extent to which jails use community Emergency Management Service (EMS) ambulances and emergency departments (EDs) to provide care. Enumerating the prevalence of health conditions, particularly traumas and ambulatory-care sensitive conditions, resulting in EMS/ED care may in turn identify opportunities to modify jail policies?both custodial and health?to diminish violence, improve health, and reduce healthcare costs. Accordingly, using a combination of prospective survey findings and analyses of statewide emergency care databases in 5 southern US states, we will examine the healthcare resources available in county jails, describe the frequency and types of conditions for which jails rely upon EMS and ED care to supplement their health services, and estimate the cost savings that jails could accrue by preventing the need for EMS, ED, and hospitalization care for ambulatory-sensitive conditions and traumas. These findings will represent a key tool in strengthening jail healthcare, improving inmate health, reducing costs, and ultimately, protecting the health of the families and communities to which inmates return